Aaron Porter… 'Did we get what we wanted? No, we didn't. But it would be wrong to say this was not a successful campaign.' Photograph: Sarah Lee for the Guardian

The last time I had anything to do with the National Union of Students, it was the early 1990s. Back then New Labour was still a twinkle in Peter Mandelson's eye, but the NUS was already ahead of the game, renouncing its Trotskyist past for a shiny new future of pragmatic professionalism – one so light on ideology as to be almost apolitical.

So the union's slick London headquarters are, I suppose, the logical conclusion of that journey. Even so, it's still quite an eye-opener to arrive and find fashionable young things bustling about like young executives, in an office that could easily pass for a Soho advertising agency. When Aaron Porter took charge as president last summer he must have looked a perfect fit – smartly dressed, geekily handsome, unencumbered by ideological baggage and bursting with media-friendly buzzwords such as "evidence-based policy". Here was a man ministers could do business with. "If vice- chancellors expect us to stand on the outside waving placards," he said at the time, "they are sorely mistaken."

Only eight months later, his presidency is over. Porter announced last week that he would not be seeking a second term in the union's April elections, the first NUS leader not to stand for re-election since 1969, having been condemned by fellow students and NUS officers as a "sell-out", a Tory and a careerist. His critics accuse him of giving into the government without a fight; of spending more time condemning violent student protesters than arguing against the tuition fee rise. At a demonstration in Manchester a month ago, he had to be led to safety by police after more than 100 protesters chased him through the streets, pelting eggs and chanting ugly taunts.

Before the battle over tuition fees began Porter had looked so impressively confident. He's one of the very few NUS presidents to have achieved a national profile while in office, appearing on Newsnight, Question Time and countless news bulletins – and when we met last week he still looks more like a smooth young lawyer than a student union hack. But beneath the suit and glasses his bearing now has the beleaguered air of a victim of bullying, battered by hostilities and more upset, I would say, than he cares to admit. There is an awful moment during the photo shoot when I realise the photographer and I are teasing him – and I wonder what we have scented to make us behave so unkindly.

For Porter personally, it's a bitter end to a presidency that had seemed to promise so much. For the wider world of student politics, the bigger question is whether his decision represents a significant shift in direction. After two decades of moderation and modern-isation, is the NUS about to become a more militant force – or is this no more than one individual's defeat?

According to Porter, the answer is neither. The NUS will elect a successor very much in his image – and his own tenure hasn't been a failure at all, he insists, but in fact a terrific success. Really? Not for nothing is the 26-year-old often described as a future MP.

When he was elected last summer he'd defined success as "ensuring that a market in fees does not emerge". Failure, he'd said, "would be a real market in fees coupled with cuts from the government". How, then, can he possibly claim to have been a success?

"I still believe we've run a successful high-profile campaign. A disastrous campaign would be one that made no impact whatsoever. This made an indelible imprint in the public's consciousness and in the political landscape. Did we get what we wanted? No, we didn't. Would I have signed up to these proposals [for trebled tuition fees]? Not in a million years. But I think it would be wrong of me to say that this was not a successful campaign. I don't think it's an exaggeration to say the coalition was under real pressure."

He describes the pledge the NUS persuaded Lib Dems to sign before the election, committing them to oppose any rise in tuition fees, as a "master- stroke". Well it would have been, I agree, if the Lib Dems had felt bound by it – but in the event they just tore it up.

"No, I still think that it was a remarkable campaign tactic, because the pledge meant that one of the parties could not run away from it." But they did run away from it, didn't they? "They did," he concedes, without missing a beat. "The preferred outcome from the pledge would've been that the Liberal Democrats stuck to it – but they didn't."

The full dividend of the Lib Dems' betrayal will come, he maintains, in four years' time at the ballot box. In the meantime: "For me, success should not be measured against what happened to tuition fees. A measure of our success is the extent to which the Liberal Democrats have been discredited. The decisions that this government take in response to young people, such as further decisions on university funding, this government will definitely think twice about that now."

If Porter is right, and the campaign will leave a lasting legacy of pressure on the coalition, his own contribution remains contentious. Critics argue that it was achieved not by the NUS, but by the protesters who invaded Millbank Tower back in November – and who were promptly condemned by Porter. Had they not stormed the building, and 50,000 students had simply marched peacefully through London, would tuition fees have developed into the high-profile issue they became?

"Well, that argument has been put to me," he concedes. "And I'm not sure, is the honest answer. I think that for every argument to say that Millbank was helpful, there's a counter argument to say that it was equally unhelpful. I've had politicians come up to me and say because of what we saw, they were more inclined to vote for the proposals."

The more Porter himself saw of rival protest organisers, the more he suspected them of deliberately encouraging students to act unlawfully – and he wanted no part of it. So a curious situation developed in which the most high-profile student protests we've seen in years were not organised or endorsed by the NUS. Does Porter think there's ever a place for illegal direct action? The question makes him look uneasy.

"Well the campaign tactics have to be proportionate to the issues that you're facing. So do I question what happened in Egypt? No I don't, I support what happened in Egypt, because there was a popular people's upraising against a dictator that was frankly abominable. But I cannot see, on the issue of tuition fees, how illegal protest is helpful."

What about if we come closer to home – does Porter think the poll tax riots were legitimate? "Well I've got more sympathy for what happened at the poll tax riots, than the violence we saw on tuition fees. I always try to see things from the bigger picture, not just thinking about students, but rather thinking about how the public perceives students." That's a remarkable thing for the president of the NUS to say, I suggest. Then he says something even more surprising.

"Well tuition fees, whilst I disagree with them, are not the biggest evil in society. It is not the worst decision that the Labour government made to introduce them, and it is not the worst decision this coalition has made to increase them. I think the decision on EMA [Education Maintenance Allowance] is much worse than on tuition fees. I think that the removal of child benefit, some of the scaling back of allowances for disabled people, the move to scale back housing benefit – I think that has a much more insidious impact on more vulnerable people than the increase of tuition fees."

Until very recently, this sort of big picture perspective from the NUS leadership might well have been regarded as a mark of maturity. But the more he talks, the more I get the impression that his timing has been rather unlucky; that student politics have changed since he was elected, and that in the new climate he comes across as not so much measured as rather innocent.

For example, he fell out with the organisers of student union occupations when he told them the NUS would provide legal support – "but these people wanted a blank cheque for all their legal costs!" – and was ambushed when he visited one occupation. "I think it was frankly disgraceful of the organisers to not tell me that they were going to present me with demands. Now if they wanted a thoughtful kind of proper engagement with someone that wants to help them out, then you don't treat someone like that. I think that they acted considerably dishonourably."

Of the scenes in Manchester last month, he says, "I wouldn't treat people that I hated like that, and I just don't think it's on. I just don't see any rationale to it." Life grew even more uncomfortable for Porter two weeks ago, when a memo he sent out to student unions was passed on to the press by a student at Exeter, and reported as a "leaked document".

"It wasn't a leak! It was a publicly available document!" he exclaims. But if he seems surprised and exasperated by the dastardliness of political intrigue, he is adamant that the overall mood and direction of student politics has not – "whatever the Guardian may think" – significantly changed.

"I speak to hundreds of students every single week, and the overwhelming majority think that NUS got the tactics spot on, that we struck the right balance. They want a credible national voice, they don't want a national organisation that's condoning violence, they don't want a national organisation that thinks that street protests are the only way of going about its business, and they don't want a national organisation saying that the way to get your issues heard is to incite the revolution. These people, the Socialist Workers party and others, their tactics are still incredibly irrelevant, outdated and frankly tired, and if these people think that's the way to get their point across then I frankly think they are deluded.

"I would also add that I think there has been a slight media agenda to pretend that these people are greater in number than they were before. If anything they're declining in overall numbers, but they've been given more of a platform. And the Guardian is at the vanguard of this. I think the Guardian has an agenda to pretend that there's some kind of revolution being fomented. But it just isn't!"

What I don't understand then, I say, is this. If Porter is convinced that student politics have not lurched to the left, and that he would be certain to win were he to stand for re-election – "Oh, without a doubt" – and he considers his own performance a success, why is he standing down?

"For me the question was about what next year would've been like. And I think that the NUS, and also me personally, need to be able to draw a line under the tuition fee debate, and I suspected that my continuation as NUS president would've inhibited us to move on from the tuition fee debate. The year would have been a postmortem of whether we did everything we needed to do, and that's not healthy for the NUS. We needed to remain on the front foot to fight the cuts and that's why I think it's best run by someone else."

It feels almost unkind to ask Porter what he will do next, as the matter of his future career prospects have weighed heavily in the criticism of his leadership. "I think there is nothing wrong with being ambitious and wanting a successful career," he says wearily. "But lots of people have made the assumption that my future lies in politics, and I don't think that's been helpful."

The charge is that he's been more concerned with ingratiating himself with politicians than standing up for students – an accusation he rejects vehemently. "I've always acted with good conscience and good faith that the decisions I've been taking are the best things for students."

Although a member of the Labour party, he stood for the NUS presidency as an independent candidate, and for all the smoothness he doesn't strike me as an intensely political person. The son of floating voters, a retired police officer and a teacher, he grew up in a house that liked to watch the Six O'Clock News, and "started getting involved in student politics because I cared about the issues, not because of any particular party." He studied English at Leicester University, where he agrees that he was a bit of a swot – "I've had lots of labels," he smiles ruefully, "and that's probably a fair one," – and lists his extracurricular activities (editor of the student newspaper, president of his hall, three part-time jobs etc) until he runs out of fingers. Then, just when he's starting to sound rather earnest, he says something terribly touching.

"The very first day at secondary school," he recalls, "the head of year seven said: 'The more you put in, the more you get out.' And that stayed with me. I didn't want to stay 12 hours in bed – what a waste, what a wasted opportunity! I was the first person in my family to go to university, and my parents had made a huge sacrifice for me to get to university. And I respect that so much, and I maybe subconsciously wanted to show some sort of gratitude for that. I just wanted to get the most out of that experience."

Porter still lives at home with his parents, and some critics have suggested that his father's career as a police officer made Porter an unduly timid protester. "I don't think I said anything that any sane minded person wouldn't say," he sighs, suddenly looking exhausted. "What were these people actually expecting the NUS president to say? Yeah, chuck another fire extinguisher off the roof? I don't think so."

So will we see more of Porter? "I hope that in 10 years' time I'm doing something that is making a sufficient impact in a positive way that means that people will carry on knowing who I am. But my motivation is not to be known," he adds hastily, "but known for doing good. I don't think I'm the kind of person to sort of drift off into obscurity."